Communication system

ABSTRACT

A communication system is disclosed in which a base station communicates with machine-type-communication (MTC) devices by dividing the base station&#39;s cell bandwidth into (non-overlapping) narrowbands. The base station identifies, based on a communication received from a communication device, a capability of that communication device to retune between narrowbands, and provides, to that communication device, control information for controlling how that communication device retunes between different narrowbands, wherein the control information is based on the identified capability of that communication device to retune between narrowbands.

TECHNICAL FIELD

The present invention relates to mobile communications devices andnetworks, particularly but not exclusively those operating according tothe 3rd Generation Partnership Project (3GPP) standards or equivalentsor derivatives thereof. The invention has particular although notexclusive relevance to data transmissions by ‘Internet of Things’devices and/or similar (narrowband) machine-type communication devices.

BACKGROUND ART

In a mobile (cellular) communications network, (user) communicationdevices (also known as user equipment (UE), for example mobiletelephones) communicate with remote servers or with other communicationdevices via base stations. In their communication with each other,communication devices and base stations use licensed radio frequencies,which are typically divided into frequency bands and/or time blocks.

The latest developments of the 3GPP standards are referred to as theLong Term Evolution (LTE) of Evolved Packet Core (EPC) network andEvolved UMTS Terrestrial Radio Access Network (E-UTRAN), includingLTE-Advanced. Under the 3GPP standards, a NodeB (or an eNB in LTE) isthe base station via which communication devices connect to a corenetwork and communicate to other communication devices or remoteservers. For simplicity, the present application will use the term basestation to refer to any such base stations. Communication devices mightbe, for example, mobile communication devices such as mobile telephones,smartphones, user equipment, personal digital assistants, laptop/tabletcomputers, web browsers, e-book readers and/or the like. Such mobile (oreven generally stationary) devices are typically operated by a user.

3GPP standards also make it possible to connect so-called ‘Internet ofThings’ (IoT) devices (e.g. Narrow-Band IoT (NB-IoT) devices) to thenetwork, which typically comprise automated equipment, such as variousmeasuring equipment, telemetry equipment, monitoring systems, trackingand tracing devices, in-vehicle safety systems, vehicle maintenancesystems, road sensors, digital billboards, point of sale (POS)terminals, remote control systems and the like. IoT devices can beimplemented as a part of a (generally) stationary apparatus such asvending machines, roadside sensors, POS terminals, although some IoTdevices can be embedded in non-stationary apparatus (e.g. vehicles) orattached to animals or persons to be monitored/tracked. Effectively, theInternet of Things is a network of devices (or “things”) equipped withappropriate electronics, software, sensors, network connectivity, and/orthe like, which enables these devices to collect and exchange data witheach other and with other communication devices. It will be appreciatedthat IoT devices are sometimes also referred to as Machine-TypeCommunication (MTC) communication devices or Machine-to-Machine (M2M)communication devices.

For simplicity, the present application refers to MTC devices in thedescription but it will be appreciated that the technology described canbe implemented on any communication devices (mobile and/or generallystationary) that can connect to a communications network forsending/receiving data, regardless of whether such communication devicesare controlled by human input or software instructions stored in memory.

MTC devices connect to the network to send data to or to receive datafrom a remote ‘machine’ (e.g. a server) or user. MTC devices usecommunication protocols and standards that are optimised for mobiletelephones or similar user equipment. However, MTC devices, oncedeployed, typically operate without requiring human supervision orinteraction, and follow software instructions stored in an internalmemory. MTC devices might also remain stationary and/or inactive for along period of time. The specific network requirements to support MTC(IoT) devices have been dealt with in 3GPP technical report (TR) 36.888V 12.0.0 and 3GPP TR 23.720 V 13.0.0. Further network requirementsrelating to MTC devices are disclosed in the 3GPP technicalspecification (TS) 22.368 V 13.1.0. The contents of these 3GPP documentsare incorporated herein by reference.

For the Release 13 (Rel-13) version of the 3GPP standards relating toMTC devices, support for a reduced bandwidth of 1.4 MHz in downlink anduplink is envisaged. Thus, some MTC devices (which may be referred to as‘reduced bandwidth MTC devices’) will support only a limited bandwidth(typically 1.4 MHz) compared to the total LTE bandwidth. This allowssuch reduced bandwidth MTC devices to be made more economically (havingfewer/simplified components) compared to MTC devices and othercommunication devices supporting a larger bandwidth and/or having morecomplicated components.

However, as LTE system bandwidths are typically larger than 1.4 MHz(i.e. up to 20 MHz), the system bandwidth is divided into a plurality of‘narrowbands’ (or ‘sub-bands’), each comprising a maximum of sixphysical resource blocks (PRBs), which is the maximum number of PRBsthat a 1.4 MHz bandwidth limited MTC device can use in LTE.

As part of the ‘enhanced’ MTC (eMTC) framework, 3GPP defined such MTCspecific narrowbands as follows:

the size of each narrowband is 6 PRBs;

the total number (NB_(whole)) of downlink (DL) narrowbands in the systembandwidth is defined as

$\begin{matrix}{{{NB}_{whole}\left\lfloor \frac{N_{RB}^{DL}}{6} \right\rfloor};} & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

the total number (NB_(whole)) of uplink (UL) narrowbands in the systembandwidth is defined as

$\begin{matrix}{{{NB}_{whole}\left\lfloor \frac{N_{RB}^{UL}}{6} \right\rfloor};} & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

the remaining resource blocks (that are not forming part of anynarrowband) are divided evenly at both ends of the system bandwidth(i.e. as equal number of RB near the lowest frequency and near thehighest frequency of the system bandwidth), with any extra odd PRB ofthe system bandwidth (e.g. in case of 3, 5, and 15 MHz system bandwidth)being located at the centre of the system bandwidth; and

the narrowbands are numbered in order of increasing PRB number.

Note:

N_(RB) ^(DL)   [Math. 3]

and

N_(RB) ^(UL)   [Math. 4]

stand for the number of PRBs in the system bandwidth (for downlink anduplink, respectively).

Since MTC devices often have simple components (especially reducedbandwidth MTC devices), their operation may also be limited. Forexample, the transceiver of an MTC device may not be able to perform afrequency retuning operation (i.e. tuning the transceiver from onefrequency band to another) in the manner specified for conventional LTEcommunication devices. Specifically, as concluded in 3GPP document no.R1-155051, it is expected that for MTC devices it will take up to twoOrthogonal Frequency Division Multiplexing (OFDM) symbols (alsoincluding the associated cyclic prefix (CP), assuming normal CP length),to retune their transceivers between different narrowband regions,during which retuning operation the MTC devices are unable to transmitor receive any data. Therefore, the related 3GPP requirements (in RAN4group) are expected to be based on a maximum retuning time of two OFDMsymbols for MTC devices. However, it is also expected that some MTCdevices (and other UEs) may be able to perform retuning within a singleOFDM symbol (including normal CP) or, if Single Carrier FrequencyDivision Multiple Access (SC-FDMA) is used, within a single SC-FDMAsymbol.

SUMMARY OF INVENTION Technical Problem

The inventors have realised that currently, for MTC devices, the basestations will always assume a maximum retuning time of two OFDM symbolsincluding CP length, as defined in the eMTC framework and relatedstandards. However, always using two symbols for retuning is notefficient and wastes valuable resources, at least for those UEs that arecapable of retuning their transceivers within a single symbol. Moreover,the amount of (unused) resources reserved for allowing retuning can growsignificantly with a large number of MTC devices (potentially in theorder of millions of MTC devices) being deployed in an operator'snetwork, resulting in large portions of network resources not beingused, even if some/many of the MTC device are capable of fast retuning,e.g. within one symbol.

Accordingly, the present invention seeks to provide systems, devices andmethods for addressing or at least alleviating these issues, whilst alsomeeting the above mentioned requirements for the provision ofnarrowbands.

Solution to Problem

In one aspect, the invention provides a base station for a communicationsystem, wherein the base station comprises: a controller for operating acell having a cell bandwidth comprising a plurality of narrowbands eachnarrowband having a respective index for identifying that narrowband;and a transceiver for communicating with a plurality of communicationdevices within the cell; wherein the controller is operable to: identifybased on a communication received, from a communication device, acapability of that communication device to retune between narrowbands;and provide, to that communication device, control information forcontrolling how that communication device retunes between differentnarrowbands, wherein the control information is based on the identifiedcapability of that communication device to retune between narrowbands.

In another aspect, the invention provides a communication device forcommunicating within a cell operated by a base station and having anassociated cell bandwidth comprising a plurality of narrowbands eachnarrowband having a respective index for identifying that narrowband,the communication device comprising: a transceiver operable to: send, tothe base station, a communication identifying a capability of thetransceiver to retune between narrowbands; and receive, from the basestation, control information for controlling how the communicationdevice retunes between different narrowbands, wherein the controlinformation is based on the identified capability of the communicationdevice to retune between narrowbands; and a controller for controllingthe transceiver when communicating data, with the base station, inaccordance with the received control information.

Aspects of the invention extend to corresponding systems, methods, andcomputer program products such as computer readable storage media havinginstructions stored thereon which are operable to program a programmableprocessor to carry out a method as described in the aspects andpossibilities set out above or recited in the claims and/or to program asuitably adapted computer to provide the apparatus recited in any of theclaims.

Each feature disclosed in this specification (which term includes theclaims) and/or shown in the drawings may be incorporated in theinvention independently (or in combination with) any other disclosedand/or illustrated features. In particular but without limitation thefeatures of any of the claims dependent from a particular independentclaim may be introduced into that independent claim in any combinationor individually.

Example embodiments of the invention will now be described by way ofexample only with reference to the attached figures in which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates a telecommunication system to whichexample embodiments of the invention may be applied;

FIG. 2 illustrates an exemplary way in which MTC device compatiblenarrowbands may be provided in the system shown in FIG. 1;

FIG. 3 is a block diagram illustrating the main components of thecommunication device shown in FIG. 1;

FIG. 4 is a block diagram illustrating the main components of the basestation shown in FIG. 1;

FIG. 5 schematically illustrates a retuning operation for MTC devices inthe system shown in FIG. 1;

FIG. 6 is an exemplary timing (signalling) diagram illustrating aprocedure followed by the MTC device and the base station according toan example embodiment of the invention;

FIG. 7 illustrates an exemplary way in which a retuning period can berealised for MTC devices in the system shown in FIG. 1;

FIG. 8 illustrates an exemplary way in which a retuning period can berealised for MTC devices in the system shown in FIG. 1;

FIG. 9 illustrates an exemplary way in which a retuning period can berealised for MTC devices in the system shown in FIG. 1;

FIG. 10 illustrates an exemplary way in which a retuning period can berealised for MTC devices in the system shown in FIG. 1.

DESCRIPTION OF EMBODIMENTS Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 in which communication devices 3 (such as mobile telephone 3-1and MTC device 3-2) can communicate with each other and/or with othercommunication nodes via an E-UTRAN base station 5 (denoted ‘eNB’) and acore network 7. As those skilled in the art will appreciate, whilst onemobile telephone 3-1, one MTC device 3-2, and one base station 5 areshown in FIG. 1 for illustration purposes, the system, when implemented,will typically include other base stations and communication devices.

The base station 5 is connected to the core network 7 via an S1interface. Although omitted from FIG. 1 for sake of simplicity, the corenetwork 7 includes, amongst others: a gateway for connecting to othernetworks, such as the Internet and/or to servers hosted outside the corenetwork 7; a mobility management entity (MME) for keeping track of thelocations of the communication devices 3 (e.g. the mobile telephone andthe MTC device) within the communication network 1; and a homesubscriber server (HSS) for storing subscription related information(e.g. information identifying which communication device 3 is configuredas a machine-type communication device) and for storing controlparameters specific for each communication device 3.

The base station 5 is configured to provide a number of controlchannels, including, for example, a physical downlink control channel(PDCCH) and a physical uplink control channel (PUCCH). The PDCCH is usedby the base station 5 for allocating resources to the communicationdevices 3 (typically by sending respective UE-specific downlink controlinformation (DCI) to each communication device that has been scheduledin the current scheduling round). The PUCCH is used by the communicationdevices 3 for sending UE-specific uplink control information (UCI) tothe base station (e.g. an appropriate HARQ Ack/Nack feedbackcorresponding to downlink data received using the resources allocated bya DCI).

In order to support such reduced bandwidth MTC devices in its cell, thesystem bandwidth of the base station 5 of FIG. 1 is divided into aplurality of non-overlapping narrowbands. The narrowbands within thesystem bandwidth are allocated such that it is possible to maintainefficient resource allocation signalling for the narrowbands for Rel-13low complexity MTC UEs.

As shown in FIG. 2, each narrowband comprises six resource blocks, andthere are some remaining resource blocks (less than six resource blocks)that are distributed evenly at the edges of the frequency bandwidth. Thesystem bandwidth comprises a total of

N_(RB) ^(DL) PRBs,   [Math. 5]

each PRB having a respective associated resource block index in therange

‘0’ to ‘N_(RB) ^(DL)−1’.   [Math. 6]

In this example, there are a total of eight narrowbands, each having arespective associated index between ‘0’ and ‘7’, numbered in order ofincreasing PRB number.

Specifically, the total number of narrowbands in the system bandwidth isdefined using the following formula:

$\begin{matrix}{{NB}_{whole}\left\lfloor \frac{N_{RB}^{DL}}{6} \right\rfloor} & \left\lbrack {{Math}.\mspace{14mu} 7} \right\rbrack\end{matrix}$

where NB_(whole) is the total number of 1.4 MHz narrowbands in thesystem bandwidth (each narrowband consisting of 6 PRBs);

N_(RB) ^(DL)   [Math. 8]

is the total number of downlink (DL) resource blocks in the systembandwidth; and

└x┘  [Math. 9]

is a flooring function (i.e. the largest integer not greater than ‘x’).

In this example, the (downlink) system bandwidth in the cell of the basestation 5 is fifty PRBs

(N_(RB) ^(DL)=50),   [Math. 10]

which corresponds to approximately 10 MHz of frequency bandwidth. Eachnarrowband comprises six PRBs (i.e. the maximum number of PRBs that abandwidth limited MTC device is capable of using). It follows thereforethat a maximum of eight whole narrowbands can be provided (i.e.NB_(whole)=8) which occupy a total of 48 PRBs of the system bandwidth.In addition, the remaining resource blocks are divided into two ‘partialnarrowbands’ each comprising one PRB (at the edges of the systembandwidth). It will be appreciated that, if appropriate, these remainingresource blocks may also be allocated to compatible MTC devices (orother user equipment). Alternatively, the remaining resource blocks maybe allocated for use by other UEs (e.g. for non-MTC use) and/or fortransmitting control data.

Beneficially, the narrowbands index numbers facilitate efficientassignment of the narrowbands to MTC devices. In this example, theindexing is arranged in order of increasing PRB number. Although notshown in FIG. 2, it will be appreciated that the partial narrowbands mayalso be provided with their own respective index numbers.

Returning now to FIG. 1, each communication device 3 may fall into oneor more of categories of UEs. A first category of UEs includeconventional (i.e. non-MTC) communication devices, such as mobiletelephones, that are capable of communicating over the entire bandwidthavailable in the cell of the base station 5. A second category of UEsinclude reduced bandwidth UEs (e.g. Rel-13 MTC devices capable of usinga 1.4 MHz bandwidth only), which are not able to communicate over theentire bandwidth available in the cell of the base station 5. UEs in thesecond category may be able to perform a retuning operation within amaximum period of two OFDM symbols. A third category of UEs includesreduced bandwidth UEs (e.g. some MTC devices/mobile telephones providedwith MTC functionality), which are configured to communicate using a 1.4MHz bandwidth only but which are able to perform a retuning operationwithin a maximum period of one OFDM symbol.

In this example, the mobile telephone 3-1 falls into the first categoryof UEs, and it may also fall into the third category of UEs (e.g. whenrunning an MTC application). Therefore, the mobile telephone 3-1 iseither able to use the entire system bandwidth at once (without anyretuning required) or it is able to perform a retuning operation(between different narrowbands) within a single OFDM symbol. On theother hand, the MTC device 3-2 falls into the second category of UEs,and it is able to perform a retuning operation within a maximum periodof two OFDM symbols.

Beneficially, the communication devices 3 in this system are configuredto notify the base station 5 about their retuning capability (i.e.whether they are capable of retuning between narrowbands within 1 or 2symbols).

In one option, each communication device 3 is configured to inform thebase station 5 about its retuning capability using radio resourcecontrol (RRC) signalling. For example, each communication device mayinclude appropriate information (e.g. a 1 bit indication/informationelement/flag) in an RRC signalling message sent to the base station 5.It will be appreciated that such retuning capability information may beadded to any suitable RRC message, such as an appropriately formattedRRC connection (re)configuration request and/or messages relating to arandom access procedure (for example, message #3 or #5 of the randomaccess procedure).

In another option, the retuning capability information (1 bitindication/flag) may be added to a message of the Feature GroupIndicator (FGI) signalling procedure.

In yet another option, it is possible to reuse existing signallinginformation (e.g. a suitable UE capability signalling normallyassociated with MTC devices) for the purpose of indicating a particularretuning capability. In other words, retuning capability information maybe provided jointly with another UE (MTC) capability information.Specifically, it will be appreciated that the existing “UL TransmissionGaps for long uplink transmissions” information element (IE), which isspecific to MTC devices, may be used to indicate whether the sendingcommunication device 3 is able to perform retuning within a singlesymbol (including normal CP). In this case, when a particularcommunication device 3 indicates to the base station 5 that it needs ULtransmission gaps for long uplink transmissions (by sending anappropriately formatted “UL Transmission Gaps for long uplinktransmissions” IE), the base station 5 may be configured to interpretthis information element to also mean that the sending communicationdevice 3 is capable of retuning within two symbols. Otherwise, the basestation 5 may be configured to assume that the sending communicationdevice 3 (which does not need UL transmission gaps for long uplinktransmissions) is capable of retuning within one symbol.

Regardless of which option is followed, the received retuning capabilityinformation may be interpreted by the base station 5 as a simple on/offtype indication (e.g. meaning that the sending UE requires a retuningperiod of two symbols when the 1 bit indication/flag is set to a certainvalue and that the sending UE requires a retuning period of one symbolwhen the 1 bit indication/flag is set to its other value). For example,communication devices 3 which fall into the first or third category ofUEs (or both) may be configured to set the 1 bit indication/flag to thevalue ‘1’/‘ON’ and communication devices 3 which fall into the secondcategory of UEs may be configured to set the 1 bit indication/flag to‘0’/‘OFF’ (or vice versa).

Therefore, the base station 5 may be configured to interpret thereceived indication/flag as follows:

‘1’ or ‘ON’: this particular UE has a transceiver that is capable ofretuning between narrowbands within a single symbol (including CP); and‘0’ or ‘OFF’: this particular UE has a transceiver that is capable ofretuning between narrowbands within two symbols (including CP).

In a particularly beneficial example, the base station 5 may beconfigured to maintain separate (dedicated) PRACH resources forcommunication devices 3 that belong to the first or third category ofUEs (MTC devices and other user equipment that are capable of retuningwithin a single symbol). Therefore, any communication device that iscapable of retuning within one OFDM symbol may be configured to transmitPRACH using such separate PRACH resources which would indicate(implicitly) to the base station 5 that the sending UE is capable ofretuning within one OFDM symbol. Similarly, MTC devices 3 that belong tothe second category of UEs (e.g. less advanced MTC devices) may beconfigured to use regular (or MTC specific) PRACH resources (if theycannot or do not wish to benefit from fast retuning). Thus, anycommunication device 3 can indicate (implicitly) to the base station 5,by using appropriate PRACH resources, whether that communication device3 is capable of retuning within one symbol or within two symbols.

Once a particular communication device indicated its retuning capabilityto the base station, the base station can beneficially allocate anappropriate frequency hopping (mirroring) pattern to that communicationdevice, taking into account whether the communication device is capableof retuning within one or two OFDM symbols. Accordingly, it is possibleto avoid or at least reduce wastage of resources for MTC devices (andother user equipment) that are capable of fast retuning (e.g. within asingle OFDM symbol) and still benefit from frequency diversity andassociated improvements (e.g. improved throughput and/or reducedinterference) that can be achieved when employing frequencyhopping/mirroring.

Beneficially, significant resource savings may also be achieved fortransmissions via the Physical Uplink Shared Channel (PUSCH) and relatedoperations at the base station. It will be appreciated that the amountof PUSCH resource saving depends on the frequency hopping periodicity(i.e. how often a particular communication device needs to hop betweennarrowbands). If the communication device is capable of retuning withinone symbol and the frequency hopping period is set to one sub-fame (i.e.Ych=1), then a resource saving of 8.6% can be achieved (for normal CPlength) in every PRB (i.e. 11/12 vs. 10/12 symbols can be used,excluding 2 symbols for RS). Beneficially, the PUSCH resource savingscales up depending on how many PRBs are allocated in a sub-frame forthe communication device. Furthermore, due to less puncturing for thePUSCH, the performance of PUSCH decoding will also be improved at thebase station.

In summary, therefore, it can be seen that in the telecommunicationsystem the serving base station is beneficially able to determine andhence know whether a particular UE/MTC device can perform retuningwithin a single OFDM/SC-FDMA symbol (including CP length), at least foruplink transmissions, or within two OFDM symbols. Hence, as a result ofthis ability to know whether or not a given UE/MTC device can performretuning within a single OFDM/SC-FDMA symbol (including CP length),significant resource savings can be achieved.

Communication Device

FIG. 3 is a block diagram illustrating the main components of thecommunication device 3 shown in FIG. 1. The communication device 3 maybe an MTC device or a mobile (or ‘cellular’) telephone configured as amachine-type communication device. The communication device 3 comprisesa transceiver circuit 31 which is operable to transmit signals to, andto receive signals from, the base station 5 via at least one antenna 33.Typically, the communication device 3 also includes a user interface 35which allows a user to interact with the communication device 3; howeverthis user interface 35 may be omitted for some MTC devices.

The operation of the transceiver circuit 31 is controlled by acontroller 37 in accordance with software stored in a memory 39. Thesoftware includes, among other things, an operating system 41, acommunications control module 42, and an MTC module 45.

The communications control module 42 controls communications between thecommunication device 3 and the base station 5 and/or other communicationnodes (via the base station 5). As shown in FIG. 3, the communicationcontrol module 42 includes, amongst others, a narrowband communicationmodule 43 and a retuning module 44.

The MTC module 45 is operable to carry out machine-type communicationtasks. For example, the MTC module 45 may (e.g. periodically) receivedata from a remote server (via the transceiver circuit 31) overresources allocated to the MTC device 3 by the base station 5. The MTCmodule 45 may also collect data for sending (e.g. periodically and/orupon detecting a trigger) to a remote server (via the transceivercircuit 31).

Base Station

FIG. 4 is a block diagram illustrating the main components of the basestation 5 shown in FIG. 1. The base station 5 comprises an E-UTRAN basestation (eNB) comprising a transceiver circuit 51 which is operable totransmit signals to, and to receive signals from, the communicationdevices 3 via one or more antennas 53. The base station 5 is alsooperable to transmit signals to and to receive signals from the corenetwork 7 via an appropriate core network interface 55 (such as an S1interface).

The operation of the transceiver circuit 51 is controlled by acontroller 57 in accordance with software stored in a memory 59. Thesoftware includes, among other things, an operating system 61 and acommunications control module 62.

The communications control module 62 controls communications with thecommunication devices 3 (including any MTC devices). The communicationscontrol module 62 is also responsible for scheduling the resources to beused by the communication devices 3 served by this base station 5. Asshown in FIG. 4, the communications control module 62 includes, amongstothers, a narrowband control module 63 and a retuning control module 64.

In the above description, the communication device 3 and the basestation 5 are described for ease of understanding as having a number ofdiscrete modules. Whilst these modules may be provided in this way forcertain applications, for example where an existing system has beenmodified to implement the invention, in other applications, for examplein systems designed with the inventive features in mind from the outset,these modules may be built into the overall operating system or code andso these modules may not be discernible as discrete entities.

The following is a description of various ways in which MTC devices mayperform a retuning operation in LTE systems.

Operation

FIG. 5 schematically illustrates an exemplary retuning operation forcommunication devices in the system shown in FIG. 1.

As shown, in this example UE1 (e.g. communication device 3-1) has beeninitially assigned to narrowband #7 (e.g. for the duration of twosub-frames), then it has to hop to narrowband #0 (e.g. for twosub-frames). The same applies to UE2 (e.g. communication device 3-2) aswell, which is initially assigned to narrowband #1, then hops tonarrowband #6. This process is also referred to as frequency mirroring,in which the frequency (narrowband) used by each communication device isregularly ‘mirrored’ around a (virtual) central line of the systembandwidth. Beneficially, such mirroring of the assigned narrowbandsimproves frequency diversity for the communication devices and hencecontributes to improved system throughput.

In the example shown in FIG. 5 the maximum retuning time betweenconsecutive narrowband regions is 2 OFDM symbols including CP length(i.e. the space between the dashed lines). However, as explained below,this retuning time may be different for different communication devices3, depending on their retuning capability.

FIG. 6 is an exemplary timing (signalling) diagram illustratingprocedures relating to signalling retuning capability of an MTC device 3to the base station 5, and employing an appropriate frequency hopping(mirroring) pattern for transmissions between that MTC device 3 and thebase station 5.

As can be seen, the procedure begins when the MTC device 3 (denoted ‘UE’in FIG. 6) indicates its retuning capability to the base station 5. Thisis generally illustrated in step S100.

As described above, there are several options for the MTC device 3 toinform the base station 5 (either explicitly or implicitly) about itsretuning capability.

Option A: UE Capability Signalling via RRC

In this option, the communication device 3 informs the base station 5about its retuning capability by generating and sending, in step S100,an RRC signalling message to the base station 5. For example, the MTCmodule 45 may be configured to check the retuning capability (stored ine.g. the retuning module 44) and provide this information to thecommunications control module 42 for generating an appropriatelyformatted RRC message.

The communication device 3 (using its communications control module 42)may include appropriate information (e.g. a 1 bit indication/informationelement/flag) in the RRC signalling message. It will be appreciated thatsuch retuning capability information may be added to any suitable RRCmessage, such as an appropriately formatted RRC connection(re)configuration request and/or the like.

The retuning capability information may comprise a 1-bit indication/flag(as part of the generated RRC message) for informing the base station 5whether or not the communication device 3 is capable of retuning withina single symbol (including CP). In other words, the communication device3 is able to instruct the base station 5 whether to turn on (or turnoff) retuning within a single symbol (at least for this particularcommunication device 3).

For example, the communication device 3 may be configured to provide RRCsignalling including one of the following values (in an appropriate 1bit indication/information element/flag):

ON (or ‘1’): the communication device 3 is capable of performing aretuning operation within a single symbol (including CP); and

OFF (or ‘0’): the communication device 3 is not capable of performing aretuning operation within a single symbol; it is capable of retuningwithin two symbols (including CP).

Option B: Reusing Existing Signalling Information

Typically, UEs that are able to perform retuning within a single symbol(including normal CP) include UEs/MTC devices that have more advancedhardware, such as XTAL oscillators, compared to less expensive crystaloscillators (TCXO). 3GPP document no. R1-166042 suggested a new UEcapability signalling called “UL Transmission Gaps for long uplinktransmissions” for providing a gap period for the UE in its uplinktransmission during which gap period the UE can switch to downlinkreception. The UE may need to switch to downlink reception (at leasttemporarily) from uplink transmission for monitoring DL referencesignals (RS) and synchronization signals (PSS/SSS) in order to estimateand correct the timing synchronization and frequency offset (beforecontinuing its uplink transmissions). It will be appreciated that UEswhich do not need UL transmission gaps for long uplink transmissions arethose with advanced hardware such as expensive XTAL oscillators andhence they are also likely to be able to perform retuning within asingle symbol (including normal CP).

Therefore, in this option, the communication device 3 and the basestation 5 are configured to reuse the existing signalling information(e.g. “UL Transmission Gaps for long uplink transmissions” and/or thelike) for the purpose of indicating the retuning capability of thecommunication device 3. It is possible to combine the UE retuningcapability indication with the existing “UL Transmission Gaps for longuplink transmissions” IE (rather than providing a separate UE retuningcapability indication).

Accordingly, if the communication device 3 is able to perform retuningwithin two symbols (including normal CP), then the communication device3 generates and sends, in step S100, an appropriately formatted “ULTransmission Gaps for long uplink transmissions” IE to the base station5. In this case, the value of the “UL Transmission Gaps for long uplinktransmissions” IE is set by the communication device 3 as follows:

OFF (or ‘0’): the communication device 3 does not need transmission gapsfor long uplink transmissions and the communication device 3 is capableof performing a retuning operation within a single symbol (includingCP); or

ON (or ‘1’): the communication device 3 needs transmission gaps for longuplink transmissions and the communication device 3 is capable ofretuning within two symbols (including CP).

Option C: Other Types of Capability Signalling

The communication device 3 may inform the base station 5 about itsretuning capability by generating and sending, in step S100, anappropriately formatted random access message. In this case, thecommunication device 3 (using its communications control module 42) mayinclude retuning capability information (e.g. a 1 bitindication/information element/flag) in message #3 or message #5 of therandom access procedure.

It will be appreciated that the retuning capability information (1 bitindication/flag) may also be added to a message sent as part of the FGIsignalling procedure.

Thus, the communication device 3 may be configured to generate and send,to the base station 5, random access and/or FGI signalling including oneof the following values (in an appropriate 1 bit indication/informationelement/flag):

ON (or ‘1’): the communication device 3 is capable of performing aretuning operation within a single symbol (including CP); and

OFF (or ‘0’): the communication device 3 is not capable of performing aretuning operation within a single symbol; it is capable of retuningwithin two symbols (including CP).

Option D: Separate Resources for PRACH (Implicit Capability Signalling)

The base station 5 may be configured to maintain separate (dedicated)PRACH resources for MTC devices 3 that are capable of retuning within asingle OFDM/SC-FDMA symbol (including CP). These resources can besignalled to the communication devices 3 in the system information block(SIB) information broadcast by the base station 5 (not shown in FIG. 6).Therefore, if the communication device 3 is capable of retuning within asingle symbol, then it transmits, in step S100, its PRACH signallingusing such pre-allocated resources, thereby informing the base station 5that the communication device 3 is capable of retuning within a singleOFDM/SC-FDMA symbol (including CP). Similarly, if the communicationdevice 3 is capable of retuning within two symbols, then it transmits,in step S100, its PRACH signalling using other than such pre-allocatedresources, which would be interpreted by the base station 5 that thiscommunication device 3 is capable of retuning within two OFDM/SC-FDMAsymbols (including CP).

Returning now to FIG. 6, after the communication device 3 sends itsretuning capability indication to the base station 5, the procedurecontinues with step S101, in which the base station 5 stores (in itsretuning control module 64) and applies (using its narrowband controlmodule 63) the retuning capability for subsequent communications withthe communication device 3.

As generally shown in step S102, the base station 5 applies anappropriate (retuning capability dependent) frequency hopping patternfor the mobile communication device 3. For example, the base station 5may configure an appropriate frequency hopping pattern for the PUCCHtransmissions for the communication device 3 (i.e. the hopping patternreserving a single OFDM symbol after each frequency hop for thecommunication device 3 if the communication device indicated that it iscapable of retuning within a single OFDM symbol; or the hopping patternreserving two OFDM symbols after each frequency hop if the communicationdevice indicated that it is capable of retuning within two OFDMsymbols).

The communication device 3 stores the received frequency hopping patternin its retuning module 44, and starts monitoring for PUCCH transmissionsby the base station 5. As generally shown in steps S103 and S103′, thebase station 5 carries out PUCCH transmissions with the configuredfrequency hopping pattern (with either one or two OFDM symbols allowedfor retuning after each hop).

The communication device 3 (using its retuning module 44) performsfrequency hopping between different narrowbands as configured via thesignalling message in step S102, and monitors for PUCCH transmissions,in each sub-frame, in the narrowband appropriate for that sub-frame.

PUCCH Retuning

FIGS. 7 to 10 illustrate exemplary ways in which an appropriate retuningperiod can be realised for MTC devices 3 in the system shown in FIG. 1.

It will be appreciated that the so-called puncturing technique may beadapted for facilitating PUCCH retuning for communication devices. Inthis case, as shown in FIG. 7, two symbols may be provided for retuning,e.g. by transmitting a punctured PUCCH Format 1a control informationfollowed by a punctured PUCCH Format 1 control information with twopunctured OFDM symbols therebetween (the first punctured OFDM symbolbeing the last symbol of the PUCCH Format 1a and the second puncturedOFDM symbol being the first symbol of the PUCCH Format 1). Although thistype of transmission may degrade PUCCH performance (since the covercodes are no longer orthogonal due to the puncturing), it still allowsMTC devices in the second UE category to perform retuning (within theretuning period represented by the two punctured symbols).

As shown in FIG. 8, puncturing may also be used to provide a retuningperiod of a single symbol (at least for compatible communicationdevices). In this case, a PUCCH Format 1a control information (with itslast symbol being punctured) is followed by a full PUCCH Format 1transmission. This arrangement improves PUCCH performance (compared tothe arrangement shown in FIG. 7) as there is no orthogonality loss atthe second sub-frame.

FIGS. 9 and 10 illustrate PUCCH transmission and retuning by employing‘RateMatching’.

In FIG. 9, two symbols are used for retuning. This is achieved bytransmitting a shortened PUCCH Format 1a control information followed bya shortened PUCCH Format 1 control information (each of which shortenedby one OFDM symbol thus effectively resulting in a combined retuningperiod of two OFDM symbols). As can be seen, the first symbol of theretuning period is the OFDM symbol immediately following the last symbolof the shortened PUCCH Format 1a and the second symbol of the retuningperiod is the OFDM symbol immediately preceding the shortened PUCCHFormat 1. Whilst this arrangement may degrade PUCCH performance (sincein some cases the cover codes are no longer orthogonal, e.g. betweenSF=4 and SF=3 for different users), it still allows MTC devices in thesecond UE category to perform retuning (within the retuning period oftwo OFDM symbols).

As shown in FIG. 10, RateMatching may also be used to provide a retuningperiod of a single symbol (at least for compatible communicationdevices). In this case, a shortened PUCCH Format 1a control informationis followed by a full PUCCH Format 1 transmission after a retuningperiod of one symbol. This arrangement improves PUCCH performance(compared to the arrangement shown in FIG. 9) as there is noorthogonality loss at the second sub-frame.

Modifications and Alternatives

Detailed example embodiments have been described above. As those skilledin the art will appreciate, a number of modifications and alternativescan be made to the above example embodiments whilst still benefitingfrom the inventions embodied therein.

It will be appreciated that although the above example embodiments havebeen described using the term ‘narrowband’ when referring to a portionof the system bandwidth, the term ‘sub-band’ may also be used.Accordingly, the term narrowband and sub-band have the same meaning andcan be used interchangeably.

It will be appreciated that although the communication system isdescribed in terms of the base station operating as a E-UTRAN basestation (eNB), the same principles may be applied to base stationsoperating as macro or pico base stations, femto base stations, relaynodes providing elements of base station functionality, home basestations (HeNB), or other such communication nodes.

In the above example embodiments, an LTE telecommunications system wasdescribed. As those skilled in the art will appreciate, the techniquesdescribed in the present application can be employed in othercommunications systems, including earlier 3GPP type systems. Othercommunications nodes or devices may include user devices such as, forexample, personal digital assistants, laptop computers, web browsers,etc.

In the example embodiments described above, the base station and thecommunication device each include transceiver circuitry. Typically, thiscircuitry will be formed by dedicated hardware circuits. However, insome example embodiments, part of the transceiver circuitry may beimplemented as software run by the corresponding controller.

In the above example embodiments, a number of software modules weredescribed. As those skilled in the art will appreciate, the softwaremodules may be provided in compiled or un-compiled form and may besupplied to the base station or the communication device as a signalover a computer network, or on a recording medium. Further, thefunctionality performed by part or all of this software may be performedusing one or more dedicated hardware circuits.

In the above example embodiments, machine-type communication devices andmobile telephones are described. However, it will be appreciated thatmobile telephones (and similar user equipment) may also be configured tooperate as machine-type communication devices. For example, the mobiletelephone 3-1 may include (and/or provide the functionality of) the MTCmodule 45.

Examples of MTC Applications

It will be appreciated that each communication device may support one ormore MTC applications. Some examples of MTC applications are listed inthe following table (source: 3GPP TS 22.368 V 13.1.0, Annex B). Thislist is not exhaustive and is intended to be indicative of the scope ofmachine-type communication applications.

TABLE 1 Service Area MTC applications Security Surveillance systemsBackup for landline Control of physical access (e.g. to buildings)Car/driver security Tracking & Tracing Fleet Management Order ManagementPay as you drive Asset Tracking Navigation Traffic information Roadtolling Road traffic optimisation/steering Payment Point of salesVending machines Gaming machines Health Monitoring vital signsSupporting the aged or handicapped Web Access Telemedicine points Remotediagnostics Remote Sensors Maintenance/Control Lighting Pumps ValvesElevator control Vending machine control Vehicle diagnostics MeteringPower Gas Water Heating Grid control Industrial metering ConsumerDevices Digital photo frame Digital camera eBook

Solutions for Non-eMTC UEs (e.g. Higher End UEs)

It will be appreciated that non-eMTC UEs may also implement eMTCfunctionality (including narrowband support, coverage enhancementtechniques, etc.) when operating under bad channel conditions. However,as such non-eMTC UEs have more complex hardware and implementations thaneMTC devices, they may still be able to retune within CP length orwithin one OFDM/SC-FDMA symbol.

In order to tailor the signalling for these types of UEs, the signallingproposed above may be modified as follows. For example, a 1-bitsignalling (ON/OFF indication/flag/IE) by the communication device canbe interpreted as follows:

ON (or ‘1’): the communication device 3 is capable of performing aretuning operation within a CP length; and

OFF (or ‘0’): the communication device 3 is capable of performing aretuning operation within a single symbol (including CP).

In this case, once the base station knows the UE capability (asindicated above) it can apply a retuning period of CP length or onesymbol. In the absence of such indication, the base station may beconfigured to apply a (default) retuning period of two symbols (at leastuntil it receives UE retuning capability information from thecommunication device). In other words, the base station may be able todistinguish between three different retuning capabilities: i) normal(LTE) retuning capability within CP length (when indicated by the UE);ii) retuning within a single OFDM symbol (e.g. for regular UEs andadvanced MTC devices, when indicated); and iii) retuning within adefault period of two OFDM symbols (e.g. for simple MTC devices, in theabsence of any indication).

The communication from the communication device to the base station,based on which the base station identifies the capability of thatcommunication device to retune between narrowbands, may comprise atleast one signalling message from the communication device (e.g. a RadioResource Control message; a message relating to a random accessprocedure; a Feature Group Indicator message; and/or the like).

The at least one signalling message may include at least one of: a flagand an appropriately formatted information element (e.g. an “ULTransmission Gaps for long uplink transmissions” information element, an“MTC retuning capability” information element, and/or the like)configured to signal to the base station whether the communicationdevice is capable of retuning between narrowbands within one symbol orwithin two symbols (e.g. Orthogonal Frequency Division Multiplexing,OFDM, symbols or Single Carrier Frequency Division Multiple Access,SC-FDMA, symbols).

The transceiver of the communication device may be operable to transmitthe communication using communication resources that depend on thecapability of the transceiver to retune between narrowbands. In thiscase, the controller of the base station may be configured to identifythe capability of that communication device to retune betweennarrowbands based on the resources used for the communication receivedfrom that communication device.

The narrowbands may each cover a different respective frequency range,and the indexes of the narrowbands may increase sequentially with thefrequency range covered by the narrowband that they represent. A numberof narrowbands in the cell bandwidth may be defined using a formula asfollows:

$\begin{matrix}{{NB}_{whole}\left\lfloor \frac{N_{RB}}{n} \right\rfloor} & \left\lbrack {{Math}.\mspace{14mu} 11} \right\rbrack\end{matrix}$

where NB_(whole) is the number of narrowbands in the cell bandwidth,N_(RB) is a number of resource blocks in the cell bandwidth, n is anumber of resource blocks in each narrowband; and

└x┘  [Math. 12]

is a floor function (i.e. the largest integer not greater than ‘x’).

The control information may identify a number of symbols (e.g.Orthogonal Frequency Division Multiplexing, OFDM, symbols or SingleCarrier Frequency Division Multiple Access, SC-FDMA, symbols) forretuning between narrowbands.

The control information may identify at least one punctured and/orshortened control format (e.g. Physical Uplink Control Channel (PUCCH)Format 1 or PUCCH Format 1 a) for retuning between differentnarrowbands.

The control information may identify a frequency hopping pattern and/ora frequency mirroring pattern.

The base station may comprise a base station of a long term evolution(LTE) radio access network. The communication may comprise amachine-type communication (‘MTC’) device which is operable tocommunicate using a reduced bandwidth compared to the cell bandwidth.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 1613407.4, filed on Aug. 3, 2016,the disclosure of which is incorporated herein in its entirety byreference.

1. A method performed by a user equipment (UE) that can communicateusing any of a plurality of narrowbands, the method comprising: sending,to a base station, information indicating a number of symbols betweentwo consecutive sub-frames for UE retuning from a first narrowband to asecond narrowband; and controlling transmissions to the base station, inaccordance with a physical uplink control channel (PUCCH) format and thenumber of symbols for UE retuning, wherein: when one symbol is used forUE retuning, in accordance with a shortened PUCCH format, the UE doesnot transmit using a last symbol in a first subframe; and when twosymbols are used for UE retuning, in accordance with the shortened PUCCHformat, the UE does not transmit using the last symbol in the firstsubframe and does not transmit using a first symbol of a secondsubframe.
 2. The method according to claim 1, wherein the informationindicating a number of symbols between two consecutive sub-frames issent using radio resource control (RRC) signalling.
 3. The methodaccording to claim 1, wherein the information indicating a number ofsymbols between two consecutive sub-frames is provided by a UEcapability information element.
 4. The method according to claim 1,further comprising receiving, based on the number of symbols between twoconsecutive sub-frames for UE retuning, control information from thebase station identifying a number of symbols for retuning betweennarrowbands.
 5. The method according to claim 1, further comprisingreceiving, based on the number of symbols between two consecutivesub-frames for UE retuning, control information from the base stationidentifying at least one punctured and/or shortened control format forretuning between different narrowbands.
 6. The method according to claim1, further comprising receiving, based on the number of symbols betweentwo consecutive sub-frames for UE retuning, control information from thebase station identifying a frequency hopping pattern and/or a frequencymirroring pattern.
 7. The method according to claim 1, wherein the UE isUE that is restricted to operate within a limited bandwidth.
 8. Themethod according to claim 1, wherein the narrowbands each cover adifferent respective frequency range, and wherein the narrowbands haveindices that are numbered in order of increasing physical resource blocknumber increase sequentially with the frequency range covered by thenarrowband that they represent.
 9. The method according to claim 8,wherein for a given cell bandwidth the number of narrowbands is definedusing a formula as follows: $\begin{matrix}{{NB}_{whole}\left\lfloor \frac{N_{RB}}{n} \right\rfloor} & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack\end{matrix}$ where NB_(whole) is the number of narrowbands in the cellbandwidth, N_(RB) is a number of resource blocks in the cell bandwidth,n is a number of resource blocks in each narrowband; and└x┘  [Math. 2] is a floor function (i.e. the largest integer not greaterthan ‘x’).
 10. A method performed by a base station that can communicatewith a user equipment (UE) using any of a plurality of narrowbands, themethod comprising: receiving, from the UE, in radio resource control(RRC) signalling, a UE capability information element indicating anumber of symbols between two consecutive sub-frames for UE retuningfrom a first narrowband to a second narrowband; and controlling the basestation, in accordance with a physical uplink control channel (PUCCH)format and the number of symbols for UE retuning, wherein: when onesymbol is used for UE retuning, in accordance with a shortened PUCCHformat, the base station does not receive transmissions from the UEusing a last symbol in a first subframe; and when two symbols are usedfor UE retuning, in accordance with the shortened PUCCH format, the basestation does not receive transmissions from the UE using the last symbolin the first subframe and does not receive transmissions from the UEusing a first symbol of a second subframe.
 11. The method according toclaim 10, wherein the base station is a base station of a long termevolution, LTE, radio access network.
 12. A computer implementableinstructions product comprising computer implementable instructions forcausing a programmable communications device to perform the method ofclaim
 1. 13. A user equipment (UE) that can communicate using any of aplurality of narrowbands, the UE comprising: a controller and atransceiver wherein the controller is operable to: control thetransceiver to send, to a base station information indicating a numberof symbols between two consecutive sub-frames for UE retuning from afirst narrowband to a second narrowband; and control transmissions tothe base station, in accordance with a physical uplink control channel(PUCCH) format and the number of symbols for UE retuning, wherein: whenone symbol is used for UE retuning, in accordance with a shortened PUCCHformat, the UE does not transmit in a last symbol in a first subframe;and when two symbols are used for UE retuning, in accordance with theshortened PUCCH format, the UE does not transmit in the last symbol inthe first subframe and does not transmit in a first symbol of a secondsubframe.
 14. A base station that can communicate with a user equipment(UE) using any of a plurality of narrowbands, the base stationcomprising: a controller and a transceiver wherein the controller isoperable to: control the transceiver to receive, from the UE, in radioresource control (RRC) signalling, a UE capability information elementindicating a number of symbols between two consecutive sub-frames for UEretuning from a first narrowband to a second narrowband; and controlreception by the transceiver, in accordance with a physical uplinkcontrol channel (PUCCH) format and the number of symbols for UEretuning, wherein: when one symbol is used for UE retuning, inaccordance with a shortened PUCCH format, the base station does notreceive transmissions from the UE in a last symbol in a first subframe;and when two symbols are used for UE retuning, in accordance with theshortened PUCCH format, the base station does not receive transmissionsfrom the UE in the last symbol in the first subframe and does notreceive transmissions from the UE in a first symbol of a secondsubframe.
 15. A system comprising: the base station according to claim13 and the user equipment.